This invention relates to switched power supplies, and more particularly to full-wave bridge power supplies.
Switching power supplies are becoming more popular for various uses, as their sizes decrease and their power-handling capabilities increase. In general, such power supplies are used to convert one direct voltage to another direct voltage, as for example might be the case when using a mains-powered rectified supply at, say, 200 volts, to a thousand or more volts, as might be required by a transmitter arrangement. Switching power supplies can also be used for reducing voltage, as for example by reducing a mains-powered rectified supply at, say, 200 volts, to 5 or 10 volts, as might be required by a computer board. Instead of a mains-powered supply, the source of the direct voltage might be a vehicular battery. The advent of all-electric and hybrid-electric vehicles gives this aspect of switched power supplies the prospect of extensive use.
The need for smaller power converters and lower weight, or, equivalently, higher power-handling capability without an increase in size, tends to drive the design of DC-to-DC converters toward operation at higher frequencies, at which the magnetic components tend to be smaller than at lower frequencies. Unfortunately, this drive toward higher frequencies tends to exacerbate losses which occur in the semiconductor switches of the converter or power supply.
FIG. 1 illustrates one type of prior-art switched power supply or DC-to-DC (DC/DC) converter. In FIG. 1, a source of direct voltage is designated 12. Source 12 connects to a first, second, third, and fourth controllable semiconductor switches 1, 2, 3, and 4, respectively. In this embodiment, the semiconductor switches are illustrated by a field-effect transistor (FET) symbol, but the switches can be of any type. In FIG. 1, controllable semiconductor switch 1 includes a main current-conducting path 1p, extending from a source 1s to a drain 1d. The current flow in the main current-conducting path 1p is controlled by the voltage or charge applied to the control electrode, illustrated as a gate 1g, all as is well known to those skilled in the art. Another controllable semiconductor switch is illustrated as 2, and it includes a main current conducting path 2p extending between a source 2s and a drain 2d, all under the control of the charge or voltage applied to a control electrode, illustrated as a gate 2g. Additional controllable semiconductor switches are illustrated as 3 and 4. Switch 3 includes a controllable path 3p extending between source 3s and drain 3d, under the control of a control electrode 3g, and switch 4 includes a controllable path 4p extending between source 4s and drain 4d, controlled by a control electrode 4g. 
In the arrangement of FIG. 1, the source 1s of switch 1 is connected to the drain 3d of switch 3 at a first node or tap 16a, and that electrode of switch 1 which is remote from the tap 16a, namely drain electrode 1d, is connected to a first terminal 121 of direct voltage source 12. Also, that electrode of the main current conducting path 3p of switch 3 is connected to the other terminal of the direct voltage power source 12. More particularly, source 3s of switch 3 is connected to terminal 122 of source 12. The arrangement of switches 2 and 4 is not dissimilar to that of switches 1 and 2. More particularly, the source 2s of switch 2 is connected to the drain 4d of switch 4 at a tap 16b. Those main current conducting path electrodes of switches 2 and 4 which are remote from tap 16b are connected to the direct voltage power supply. Thus, drain electrode 2d of switch 2 is connected to terminal 121 of supply 12, and the source electrode 4s of switch 4 is connected to terminal 122 of supply 12. As known to those skilled in the art, there are several ways to control the switching of the various switches of the power supply of FIG. 1, so that an alternating voltage appears across taps 16a and 16b, where the word xe2x80x9cacrossxe2x80x9d means that a voltage difference appears xe2x80x9cbetweenxe2x80x9d the terminals, however the terminals may be physically arranged.
The alternating voltage appearing across the taps 16a and 16b of the power supply of FIG. 1 is coupled to the primary winding 14p of a transformer arrangement 14. Transformer arrangement 14 also includes at least one secondary winding, illustrated as a center-tapped secondary winding 14s. Winding 14s is connected to a rectifier and filter arrangement including diodes or rectifiers designated D1 and D2, and a filter including a series inductor L and a shunt capacitor C. The output direct voltage of the arrangement of FIG. 1 is a voltage designated Vo, produced xe2x80x9cacrossxe2x80x9d (again, not a term relating to physical location) capacitor C for application to a load, represented by a resistor R.
Those skilled in the art know that there are several ways to control the controllable switches 1, 2, 3, and 4 of FIG. 1 in order to generate the desired alternating voltage across the primary winding 14p of FIG. 1. These various techniques have various advantages and disadvantages, and some may be more desirable at various states of the technology than others. Some of these techniques are described in U.S. Pat. No. 4,811,184, issued Mar. 7, 1989 in the name of Koninsky et al.; 4,688,165, issue Aug. 18, 1987 in the name of Pruitt; 4,691,270, issued Sep. 1, 1987 in the name of Pruitt; 4,761,722, issued Aug. 2, 1988 in the name of Pruitt; 5,451,962, issued Sep. 19, 1995 in the name of Steigerwald; 5,684,683, issued Nov. 4, 1997 in the name of Divan et al. An article entitled Design Review: 100 W, 400 kHz, DC/DC Converter With Current Doubler Synchronous Rectification Achieves 92% Efficiency, by Laszlo Balogh, gives an overview of various types of switch control. One of the types of switch control which is currently advantageous is the phase-shift control, in which the control electrode drive signals are relatively phase shifted so that intervals of conduction of one switch pair of a bridge, such as switch pair 1,3, to apply power to the transformer, are separated by intervals in which another switch pair, such as switch pair 1,2, are conductive, and no power is applied to the transformer.
FIG. 2a is a representation of the sequence of states of operation of the converter or power supply of FIG. 1 following a phase shift control pattern. FIGS. 2b, 2c, 2d, and 2e (FIGS. 2a through 2e or FIGS. 2a-2e) are time plots of ON (main current conducting path conductive) and OFF (main current conducting paths nonconducting) times of controllable semiconductor switches 1, 2, 3, and 4, respectively, of FIG. 1. FIG. 2f is a time plot 206 of the voltage applied to the primary winding 14p of the transformer 14 of FIG. 1, FIG. 2g is a time plot of the magnetizing current IM in the primary winding 14p of transformer 14 of FIG. 1 in response to the applied voltage of FIG. 2f. FIG. 2h is an amplitude-time plot illustrating the total current in the transformer 14 of FIG. 1, including magnetizing current and load current portions; during the first state in the interval t0-t1, the current is in a first direction, indicated as xe2x80x9cupwardxe2x80x9d in FIG. 2h. FIG. 2j is a plot of the current in filter inductor L of FIG. 1. The first state illustrated in FIG. 2a is state S1, which extends from time t0 to a later time t1. In state S1, switches 1 and 4 are ON or conducting, as indicated by the logic xe2x80x9chighxe2x80x9d or xe2x80x9c1xe2x80x9d level of the gate signals 201 and 204 of FIGS. 2b and 2e, respectively. As a consequence, current flows from terminal 121 of supply 12 of FIG. 1, through the main current carrying path 1p of switch 1, through the primary winding 14p of transformer 14, and through the main current carrying path 4p of controllable semiconductor switch 4 to the other terminal, namely terminal 122, of direct voltage source 12. During the state-1 interval extending from t0 to t1, controllable semiconductor switches 2 and 3 are nonconductive, as suggested by the logic xe2x80x9clowxe2x80x9d or xe2x80x9c0xe2x80x9d level of their control electrode signals 202 and 203 of FIGS. 2c and 2d, respectively. During the first-state interval t0 to t1, the magnetizing current in the transformer 14 increases steadily or monotonically, as suggested by IM plot 208 of FIG. 2g. Also during the first-state interval t0 to t1, the total current IT in the transformer 14 increases, following the magnetizing current, but also including a portion responsive to the load current. Further during state-1 interval t0 to t1 of FIGS. 2i and 2j, transformer 14 of FIG. 1 produces an output voltage, illustrated by plot 212 of FIG. 2i, for rectification by one of diodes D1 and D2 of FIG. 1, which in turn results in the increasing current 214 of FIG. 2j in inductor L of FIG. 1.
During the second state S2 of FIG. 2a, extending from time t1 to time t2, controllable switches 1 and 2 of FIG. 1 are ON or conductive, while switches 3 and 4 are OFF or nonconductive. The ON states are indicated by the high states of plots 201 and 202 of FIGS. 2b and 2d, respectively. The OFF states are indicated by the low states of plots 203 and 204 of FIGS. 2c and 2e, respectively. With switches 3 and 4 OFF, no current can flow from direct voltage source 12, and no power can be transferred to the load. Consequently, the only source of energy to maintain conduction in any of the switches of FIG. 1 is the magnetizing or inductive current flowing in transformer 14. This magnetizing current continues to flow in the loop including conductive controllable semiconductor switches 1 and 2. Since switches 1 and 2 are conductive, their ON-state resistance is low, and little voltage is occasioned by the flow of the magnetizing current in the loop. Consequently, the magnetizing current flow continues with little power loss, so the does not decrease markedly in the interval t1-t2, as illustrated by plot 208 of FIG. 2g. The current through inductor L of FIG. 1, however, must provide power to the load, so its current decreases in the second-state interval t1-t2, as illustrated by plot 210 of FIG. 2h. 
State S2 of FIG. 2a changes to state S3 at time t2, with controllable semiconductor switch 1 turning OFF and switch 3 turning ON, while switch 2 remains ON and switch 4 remains OFF. In this state, the full direct voltage from source 12 is applied across the main current carrying path 1p of switch 1, and current begins to flow through the primary winding 14p in the xe2x80x9coppositexe2x80x9d or second direction relative to the direction of flow immediately before time t2, as indicated by plot 210 of FIG. 2h. During state 3, in the interval T2-t3, the magnetizing current of transformer 14 decreases to zero, and then again increases in the opposite polarity, as indicated by plot 208 of FIG. 2g, and the total current continues to increase, as can be seen from plot 210 of FIG. 2g. State S3 changes to state S4 at time t3, with the turning OFF of switch 2 and turning ON of switch 4, as suggested by their gate voltages 202 and 204 of FIGS. 2c and 2e, respectively. In state S4, switches 1 and 2 are OFF or nonconductive, and switches 3 and 4 are ON or conductive, to form a loop through which substantially constant magnetizing current can flow in the interval t3-t4, as indicated by plot 208 of FIG. 2g. Finally, the state of the system reverts to the first state S1 at time t4, corresponding to a new time t0, with the opening of switch 3 and closing of switch 1.
Improved switching power supplies are desired.
A full-wave bridge switching power supply according to a general aspect of the invention includes first and third xe2x80x9cseriallyxe2x80x9d connected switches, and second and fourth xe2x80x9cseriallyxe2x80x9d connected switches. An output transformer has one end of its primary winding connected to the juncture of the first and third switches and the other end connected to the juncture of the second and fourth switches. The switches are provided, by way of transformers, with zero-voltage switching signals. In order to avoid the switch-slowing effects of transformer inductance, a subsidiary power supply is associated with each switch. The subsidiary power supplies of the first and third switches are coupled to the control electrodes (gates) of the first and third switches at turn-on, and the subsidiary power supplies of the second and fourth switches are applied during turn-off.
A full-wave switching power supply according to somewhat more specific hypostasis of the invention includes first, second, third, and fourth controllable switches, each of which includes a control electrode and a controlled current conducting main path. A bridge type of connection is provided by means connecting a first end of the main path of the first controllable switch to a second end of the main path of the third controllable switch to thereby define a first tap point, and further means connecting a first end of the main path of the second controllable switch to a second end of the main path of the fourth controllable switch, to thereby define a second tap point. An output transformer includes a primary winding coupled to the first and second tap points, for being driven, during operation, with alternating voltage appearing thereacross. A zero-voltage switching signal generator drives the controllable switches in zero-voltage fashion. A drive transformer arrangement is coupled to the zero-voltage switching signal generating means and to the control electrodes of the first, second, third, and fourth controllable switches. First, second, third and fourth subsidiary power supplies are coupled to secondary windings of the drive transformer arrangement, for generating subsidiary direct voltages in response to the switching signals. First, second, third, and fourth control electrode switches are coupled to the first, second, third, and fourth subsidiary power supplies, respectively, and to the control electrodes of the first, second, third, and fourth controllable switches, respectively, for coupling the first and third subsidiary direct voltages to the control electrodes of the first and third controllable switches, respectively, during their respective turn-on intervals, and for coupling the second and fourth subsidiary direct voltages to the control electrodes of the second and fourth controllable switches, respectively, during their respective turn-off intervals.
A full-wave switching power supply according to an aspect of the invention includes a source of direct voltage. The source of direct voltage defines first and second terminals. The power supply also includes a first controllable semiconductor switch including a main current conducting path and a control electrode, and a third controllable semiconductor switch including a main current conducting path and a control electrode. The current conducting paths of the first and third controllable semiconductor switches are coupled together to define a first tap point. That end of the main current conducting path of the first switch which is remote from the first tap point is coupled to the first terminal of the source of direct voltage, and that end of the current conducting path of the third controllable switch which is remote from the first tap point is coupled to the second terminal of the source of direct voltage. The power supply also includes a second controllable semiconductor switch including a main current conducting path and a control electrode, and a fourth controllable semiconductor switch including a main current conducting path and a control electrode. The current conducting paths of the second and fourth switches are coupled together to define a second tap point. That end of the main current conducting path of the second switch which is remote from the second tap point is coupled to the first terminal of the source of direct voltage, and that end of the current conducting path of the fourth switch which is remote from the second tap point is coupled to the second terminal of the source of direct voltage. The power supply also includes switching control means for generating switching signals for control of the control electrodes of the first, second, third and fourth controllable semiconductor switches in such a manner that (a) in a first state following a fourth state, the first and fourth switches are conductive, and the second and third switches are nonconductive, (b) in a second state immediately following the first state, the first and second switches are conductive, and the third and fourth switches are nonconductive, (c) in a third state immediately following the second state, the second and third switches are conductive, and the first and fourth switches are nonconductive, and (d) during the fourth state, immediately preceding the first state, the third and fourth switches are conductive, and the first and second switches are nonconductive. A first transformer arrangement includes a primary winding coupled to the switching control means, and also includes first and second secondary windings across which a first set of the switching signals are generated. A second transformer arrangement includes a primary winding coupled to the switching control means, and also includes first and second secondary windings across which a second set of the switching signals are generated. A first subsidiary power supply is coupled to the first secondary winding of the first transformer arrangement, for producing a first subsidiary direct voltage in response to the switching signals. A third subsidiary power supply is coupled to the second secondary winding of the first transformer arrangement, for producing a third subsidiary direct voltage in response to the switching signals. A second subsidiary power supply is coupled to the first secondary winding of the second transformer arrangement, for producing a second subsidiary direct voltage in response to the switching signals. A fourth subsidiary power supply is coupled to the second secondary winding of the second transformer arrangement, for producing a fourth subsidiary direct voltage in response to the switching signals. A first drive switching means is coupled to the first and second subsidiary power supplies, and to the first and second secondary windings of the first transformer arrangement, and to the control electrodes of the first and third controllable semiconductor switches, for coupling the first and third subsidiary direct voltages to the control electrodes of the first and third controllable semiconductor switches, respectively, during their respective turn-ON intervals, for charging the control electrodes of the first and third controllable semiconductor switches, respectively. A second controllable drive switching means includes control electrodes coupled to the second and third subsidiary power supplies and to the first and second secondary windings of the second transformer arrangement, and also includes switched conduction paths coupled to the control electrodes of the second and fourth controllable semiconductor switches and to the second tap point, for, in response to switching signals, coupling the second and fourth subsidiary direct voltages to the control electrodes of the second controllable drive switching means, for thereby discharging the control electrodes of the second and fourth controllable semiconductor switches. First control electrode discharge means is coupled to the control electrodes of the first and third controllable semiconductor switches, and also coupled to the first and second secondary windings of the first transformer arrangement, for discharging the control electrodes of the first and third controllable semiconductor switches during their respective turn-off periods, without applying to the control electrodes the subsidiary direct voltages from the first and third subsidiary power supplies. Second control electrode charging means is coupled to the control electrodes of the second and fourth controllable semiconductor switches, and also coupled to the first and second secondary windings of the second transformer arrangement, for charging the control electrodes of the second and fourth controllable semiconductor switches during their respective turn-ON intervals, without applying to the control electrodes the subsidiary direct voltages from the second and fourth subsidiary power supplies.
A switching power supply according to another aspect of the invention is for producing alternating voltage from a source of direct voltage, where the source of direct voltage includes first and second power terminals. The power supply comprises a power transformer which includes a primary winding defining first and second ends, and also defining a secondary winding at which the alternating voltage is produced. The switching power supply also includes first, second, third, and fourth power switches, each includes a main current conducting path and a control electrode. The first and third power switches have their main current conducting paths coupled together to define a first tap point. The first tap point is coupled to the first terminal of the primary winding of the power transformer. The second and fourth power switches have their main current conducting paths coupled together to define a second tap point. The second tap point is coupled to the second terminal of the primary winding of the power transformer. That end of the main current conducting path of the first power switch which is remote from the first tap point is coupled to the first power terminal of the source of direct voltage. That end of the main current conducting path of the third power switch which is remote from the first tap point is coupled to the second power terminal of the source of direct voltage. That end of the main current conducting path of the second power switch which is remote from the second tap point is coupled to the first power terminal of the source of direct voltage. That end of the main current conducting path of the fourth power switch which is remote from the second tap point is coupled to the second power terminal of the source of direct voltage. Taken together, these connections define a full-wave bridge structure. The switching power supply according to this other aspect of the invention also includes a source of zero-voltage switching signals for controlling a full-wave bridge for zero-voltage switching. A first transformer arrangement includes a primary winding coupled to the source of switching signals, and also includes first and second secondary windings, for coupling switching signals to the control electrodes of the first and third power switches. A first subsidiary power supply is coupled to the first secondary winding of the first transformer arrangement, for producing a first subsidiary direct voltage, relative to the first tap, in response to the switching signals. A third subsidiary power supply is coupled to the second secondary winding of the first transformer arrangement, for producing a third subsidiary direct voltage, relative to the second terminal of the source of direct voltage, also in response to the switching signals. A first control electrode or gate turn-on control switch arrangement is coupled to the first subsidiary power supply and to the control electrode of the first power switch, for applying the first subsidiary direct voltage to the control electrode of the first power switch in response to a turn-on portion of the zero-voltage switching signals applied to the first transformer arrangement. A first control electrode turn-off control switch arrangement is coupled to the control electrode of the first power switch and to the first tap point, for discharging the control electrode of the first power switch in response to a turn-off portion of the switching signals applied to the first transformer arrangement. A third control electrode turn-on control switch arrangement is coupled to the third subsidiary power supply and to the control electrode of the third power switch, for applying the third subsidiary direct voltage to the control electrode of the third power switch in response to a turn-on portion of the switching signals applied to the first transformer arrangement. A third control electrode or gate turn-off control switch arrangement is coupled to the control electrode of the third power switch and to the second terminal of the source of direct voltage, for discharging the control electrode of the third power switch in response to a turn-off portion of the switching signals applied to the first transformer arrangement.
The switching power supply according to this other aspect of the invention also comprises a second transformer arrangement including a primary winding coupled to the source of switching signals, and also includes first and second secondary windings, for receiving switching signals for coupling to the control electrodes of the second and fourth power switches. A second subsidiary power supply is coupled to the first secondary winding of the second transformer arrangement, for producing, in response to the switching signals, a second subsidiary direct voltage, relative to the second tap. A fourth subsidiary power supply is coupled to the second secondary winding of the second transformer arrangement, for producing a fourth subsidiary direct voltage, relative to the second terminal of the source of direct voltage, also in response to the switching signals. A second control electrode or gate turn-on control switch arrangement is coupled to the first terminal of the first secondary winding of the second transformer arrangement, for supplying charge to the second control electrode of the second switching arrangement during a turn-on portion of the switching signals. A second control electrode turn-off control switch arrangement is coupled to the second subsidiary power supply and to the control electrode of the second power switch, for applying the second subsidiary direct voltage to the control electrode of the second power switch in response to a turn-off portion of the switching signals applied to the second transformer arrangement. A fourth control electrode gate or gate turn-on control switch arrangement is coupled to the first terminal of the second secondary winding of the second transformer arrangement, for supplying charge to the control electrode of the fourth switching arrangement during a turn-on portion of the switching signals applied to the second transformer arrangement. A fourth control electrode turn-off control switch arrangement is coupled to the fourth subsidiary power supply and to the control electrode of the fourth power switch, for applying the fourth subsidiary direct voltage to the control electrode of the fourth power switch in response to a turn-off portion of the switching signals applied to the second transformer arrangement.
In a particular embodiment of this other aspect of the invention, the switching power supply further includes a second end of the first secondary winding of the first transformer arrangement electrically connected to the first tap point, and the first subsidiary power supply includes a first rectifier and a first capacitor coupled to the first secondary winding of the first transformer arrangement, for producing the first subsidiary direct voltage across the first capacitor in response to the switching signals. The third subsidiary power supply of this particular embodiment also further includes a third rectifier and a third capacitor coupled to the second secondary winding of the first transformer arrangement, for producing a third subsidiary direct voltage across the third capacitor in response to the switching signals. The first control electrode turn-on control switch arrangement is coupled to a terminal of the first capacitor and to the control electrode of the first power switch, and the third control electrode turn-on control switch arrangement is coupled to a terminal of the third capacitor, and to the control electrode of the third power switch.
In a particular avatar of the particular embodiment, the first capacitor includes one electrode connected to the second terminal of the first secondary winding of the first transformer arrangement and to the first tap point, and a second electrode connected to a terminal of the first rectifier, the second capacitor includes one electrode coupled to the second terminal of the first secondary winding of the second transformer arrangement, the third capacitor includes one electrode coupled to a second terminal of the second secondary winding of the first transformer arrangement, and the fourth capacitor includes one electrode coupled to the second terminal of the second secondary terminal of the second transformer arrangement.
In a particular hypostasis of this avatar of the power supply, the first control electrode turn-on control switch arrangement includes a control electrode, which control electrode is coupled to the first terminal of the first secondary winding of the first transformer arrangement, the third control electrode turn-on control switch arrangement includes a control electrode, which control electrode is coupled to the second terminal of the source of direct voltage, the second control electrode turn-off control switch arrangement includes a control electrode, which control electrode is coupled to the first terminal of the first secondary winding of the second transformer arrangement, and the fourth control electrode turn-off control switch arrangement includes a control electrode, which control electrode is coupled to the first terminal of the second secondary winding of the second transformer arrangement.